A number of serious medical conditions may be treated in a minimally invasive manner with various kinds of catheters designed to reach treatment sites internal to a patient's body. One such medical condition is atrial fibrillation—a serious medical condition that results from abnormal electrical activity within the heart. This abnormal electrical activity may originate from various focal centers of the heart and generally decreases the efficiency with which the heart pumps blood. It is believed that some of these focal centers reside in the pulmonary veins of the left atrium. It is further believed that atrial fibrillation can be reduced or controlled by structurally altering or ablating the tissue at or near the focal centers of the abnormal electrical activity.
One method of ablating tissue of the heart and pulmonary veins to control atrial fibrillation includes delivering radio-frequency (RF) energy to the tissue to be ablated. In particular, high frequency energy can be employed, for example, to cause ionic agitation and frictional heat in targeted tissue, causing permanent damage to the tissue. Once damaged, the tissue may no longer propagate or source electrical signals, and the fibrillation may be treated or reduced. The RF energy can be delivered by an RF catheter having an RF source at a distal treatment end that is positioned at a treatment site inside a patient during a treatment procedure.
Another method of ablating tissue of the heart and pulmonary veins to control atrial fibrillation includes delivering cryotherapy to the tissue to be ablated. Cryotherapy may also cause permanent alteration to treated tissue, preventing the treated tissue from propagating or sourcing electrical signals, thereby reducing or eliminating atrial fibrillation. Cryotherapy may be delivered to appropriate treatment sites inside a patient's heart and circulatory system by a cryotherapy catheter. A cryotherapy catheter generally includes a treatment member at its distal end, such as an expandable balloon or metal tip having a cooling chamber inside. A cryotherapy agent may be provided by a source external to the patient at the proximal end of the cryotherapy catheter and delivered distally, through a lumen in an elongate member, to the cooling chamber where it is released. Release of the cryotherapy agent into the chamber cools the chamber, the balloon's outer surface, and tissue that is in contact with the outer surface, to perform ablation. The cryotherapy agent may be exhausted proximally through an exhaust lumen in the elongate member to a reservoir external to the patient.